Investigations on Structural and Transport Properties of Mixed Oxide Systems

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Single Phase Synthesis; Neutron Diffraction and Dielectric Studies on 0.6PbFe0.5Nb0.5O3-0.4BiFeO3 Multiferroic

0.6Pb(Fe0.5Nb0.5)O3-0.4BiFeO3 (0.6PFN-0.4BFO) multiferroic solid solution was synthesized by single step solid state reaction method. The optimized synthesis parameters for 0.6PFN-0.4BFO multiferroic was calcination at 700 °C /2 hr and sintering at 800 °C /3 hr. Single phase was confirmed though room temperature X-ray Diffraction (XRD) and room temperature Neutron Diffraction (ND). XRD and ND data were well fitted with monoclinic structure with Cm space group. The magnetic structure was refined using the propagation vector k = (0.5; 0.5; 0.5) and the structure was found to be G-type antiferromagnetic. The dielectric constant and loss tangent of 0.6PFN-0.4BFO shows the frequency and temperature dependent nature. Loss tangent exhibits the thermally dependent relaxation peaks. 0.6PFN-0.4BFO is a potential candidate for above room temperature applications

Ce4Ag3Ge4O0.5 - chains of oxygen-centered OCe2Ce2/2] tetrahedra embedded in a CeAg3Ge4] intermetallic matrix

The oxidation of an intermetallic phase under high-pressure/high-temperature conditions led to the synthesis of Ce4Ag3Ge4O0.5 exhibiting OCe2Ce2/2] tetrahedral chains, in which the oxygen atoms statistically occupy the tetrahedral centres. Starting from a 1 : 1 : 1 CeAgGe precursor (NdPtSb type), a multianvil high-pressure/high-temperature experiment at 11.5 GPa and 1250-1300 degrees C revealed Ce4Ag3Ge4O0.5, crystallizing in the space group Pnma with the following lattice parameters: a = 2087.3(4), b = 439.9(1), and c = 1113.8(2) pm. Magnetic measurements showed Curie-Weiss behavior above 100 K with an experimental magnetic moment of 2.42 mu B per Ce atom, close to the value for the free Ce3+ ion, clearly indicating trivalent cerium in Ce4Ag3Ge4O0.5. Full potential GGA+U band structure calculations resulted in metallic properties and a magnetic ground state with one unpaired 4f-electron per cerium in agreement with the experiments

Ferromagnetic Ordering in the Thallide EuPdTl 2

The new thallide EuPdTl 2 , synthesized from the elements in a sealed tantalum tube in a highfrequency furnace, was investigated by X-ray diffraction on powders and single crystals: MgCuAl 2 type, Cmcm, Z = 4, a = 446.6(1), b = 1076.7(2), c = 812.0(2) pm, wR2 = 0.0632, 336 F 2 values, 16 variables. The structure can be considered as an orthorhombically distorted, palladium-filled variant of the binary Zintl phase EuTl 2 . The palladium and thallium atoms build up a three-dimensional [PdTl 2 ] polyanion with significant Pd-Tl (286 -287 pm) and Tl-Tl (323 -329 pm) interactions. The europium atoms fill distorted hexagonal channels of the [PdTl 2 ] polyanion. Susceptibility measurements show a magnetic moment of 7.46(5) µ B /Eu atom, indicative of divalent europium. EuPdTl 2 is a soft ferromagnet with a Curie temperature of T C = 12.5(5) K

Magnetic order in the frustrated Ising-like chain compound Sr3_3NiIrO6_6

We have studied the field and temperature dependence of the magnetization of single crystals of Sr3NiIrO6. These measurements evidence the presence of an easy axis of anisotropy and two anomalies in the magnetic susceptibility. Neutron powder diffraction realized on a polycrystalline sample reveals the emergence of magnetic reflections below 75 K with magnetic propagation vector k ~ (0, 0, 1), undetected in previous neutron studies [T.N. Nguyen and H.-C zur Loye, J. Solid State Chem., 117, 300 (1995)]. The nature of the magnetic ground state, and the presence of two anomalies common to this family of material, are discussed on the basis of the results obtained by neutron diffraction, magnetization measurements, and symmetry arguments

Investigation on structural, Mossbauer and ferroelectric properties of (1-​x)​PbFe0.5Nb0.5O3-​(x)​BiFeO3 solid solution

(1-​X)​PbFe0.5Nb0.5O3(PFN)​-​(x)​BiFeO3(BFO) multiferroic solid solns. with x = 0.0, 0.1, 0.2, 0.3 and 0.4 were synthesized through single step solid state reaction method and characterized thoroughly through x-​ray Diffraction (XRD)​, SEM, Fourier Transform Infra-​Red (FTIR)​, Raman, Mossbauer spectroscopy and ferroelec. studies. The room temp. (RT) XRD studies confirmed the formation of single phase with negligible amt. of secondary phases (x = 0.2 and 0.4)​. The zoomed XRD patterns of (1-​x)​PFN-​(x)​BFO solid solns. showed the clear structural phase transition from monoclinic (Cm) to rhombohedral (R3c) at x = 0.4. The Raman spectra of the (1-​x)​PFN-​(x)​BFO solid solns. showed the compn. dependent phase transition from monoclinic (Cm) to rhombohedral (R3c)​. With increasing x in PFN, the modes related monoclinic symmetry changes to those of rhombohedral symmetry. The RT Mossbauer spectroscopy results evidenced the existence of compn. dependent phase transition from paramagnetic to weak antiferromagnetic ordering and weak antiferromagnetic to antiferromagnetic ordering. The Mossbauer spectroscopy showed paramagnetic behavior with a doublet for x = 0.0, 0.1 and 0.2 are shows the weak antiferromagnetic with paramagnetic ordering. For x = 0.3 and 0.4 shows the sextet pattern and it is a clear evidence of antiferromagnetism. The ferroelec. (P-​E) loops at RT indicate small polarization, as the x concn. increases in PFN, the remnant polarization and coercive field were decreased, which may due to the increase in the cond. and leaky behavior of the samples

Stability of geometrically frustrated magnetic state of Ca3CoRhO6 to applications of positive and negative pressure

The influence of negative chemical pressure induced by gradual replacement of Ca by Sr as well as of external pressure (up to 10 kbar) on the magnetism of Ca3CoRhO6 has been investigated by magnetization studies. It is found that the solid solution, Ca(3-x)Sr(x)CoRhO6, exists at least till about x= 1.0 without any change in the crystal structure. Apart from insensitivity of the spin-chain feature to volume expansion, the characteristic features of geometrical frustration interestingly appear at the same temperatures for all compositions, in sharp contrast to the response to Y substitution for Ca (reported previously). Interestingly, huge frequency dependence of ac susceptibility known for the parent compound persists for all compositions. We do not find a change in the properties under external pressure. The stability of the magnetic anomalies of this compound to the volume change (about 4%) is puzzling